Natural and synthetic derivatives of vitamin A (retinoids), are active in cancer therapy and chemoprevention. Mechanisms involved in these clinical effects and why retinoid resistance occurs need to be better understood. This is the objective of this revised NIH R01-CA87546 competing renewal application that examines comprehensively, use of classical and non-classical retinoids as tools to uncover chemopreventive mechanisms. Work from the prior finding cycle revealed that all- trans-retinoic acid (RA) prevented tobacco-carcinogenic transformation of human bronchial epithelial (HBE) cells through novel mechanisms. These involved proteasomal degradation of cyclin D1 and transcriptional repression of the epidermal growth factor receptor (EGFR) that each repressed cyclin D1. The resulting G1 arrest permitted repair of carcinogenic damage to DNA and thereby conferred chemoprevention. Cyclin D1 was a molecular target for both pathways. Notably, these pathways were each deregulated in RA-resistant HBE cells that we derived and found to exhibit retinoic acid receptor-beta (RARbeta) silencing, as often occurs in lung carcinogenesis. A novel RARbeta isoform was also discovered that could account for clinical retinoid resistance. Notably, retinoid X receptor (RXR) agonists (rexinoids) by-passed this RARbeta3 block and activated similar down-stream pathways as classical retinoids to repress cyclin D1. The specific aims will: (1) comprehensively explore using cultured HBE and lung cancer cells that are sensitive or resistant to all-trans-retinoic acid (RA) whether transcriptional or post-transcriptional chemopreventive mechanisms engaged by classical or non-classical retinoids confer D-type cyclin repression. Function of the novel RARbeta isoform will be studied. Whether cooperation with demethylation agents restores RARbeta expression and retinoid response and whether repressing D-type cyclins by siRNA targeting or EGFR inhibition enhances retinoid or rexinoid response will be learned. (2) Studies that target for chemoprevention D-type cyclins in carcinogen-induced and transgenic mouse models will be conducted. (3) Findings will be translated to the clinic using unique tissues harvested from proof of principle trials that target D-type cyclins. These trials are yielding exciting preliminary findings that validate D-type cyclins as chemopreventive targets. Unique pre-clinical and clinical models and resources are available. Successful achievement of these aims will improve understanding how classical or non-classical retinoids exert chemopreventive effects. These findings would translate this work from the bench to the bedside to advance a mechanism-based approach to cancer chemoprevention.